In order to obtain information on the biology of the masked chafer, Cyclocephala paraguayensis Arrow (Scarabaeidae: Dynastinae: Cyclocephalini), and its immature morphology, the beetle life cycle was studied under laboratory conditions. After field collection, adults were placed inside containers filled with soil obtained in the original capture to provide an oviposition site after mating ocurred. Eggs were collected daily and isolated for manipulation experiments and life cycle observations. Detailed information about the eggs, instars and life cycle duration, and morphological features of immature stages were noted and examined. Egg viability was higher in the “nonmanipulated” batch. The complete ontogenic cycle of C. paraguayensis was 171 ± 11 days (n = 7). Despite the records of Cyclocephala being crop pests, reared larvae of C. paraguayensis thrived and developed into well-formed, fertile adults on an entirely saprophagous diet, indicating that they are not rhizophagous in the wild. The third instar can be distinguished from the other species mainly by the following unique characters: maximum width of the head capsule, distal antennal setae, and bifurcated setae on the raster.